Free MCAT Practice Question – Biology

by Kerry Goldstein

May 10, 2013

MCAT Biology, MCAT Blog, MCAT Long Form, MCAT Prep

In terms of sheer quantity of information you need to memorize for the MCAT, nothing beats the biology portion of the Biological Sciences section. While you may feel more comfortable with bio (the most common major among MCAT test-takers), you can’t be complacent: everyone else in the room is ALSO a bio major. If you’re going to out-compete them, you’ve gotta hit the books hard.

The test will most directly assess your ability to recall and apply basic bio concepts in the discrete questions. Here’s an example:

Item 17

A lipase is an enzyme responsible for breaking down ingested fats and is normally found in an area that is at normal body temperature. If the enzyme were placed in a beaker with fat molecules that was initially at room temperature and the temperature were gradually increased, what would happen to enzyme activity?

A) Enzyme activity would steadily increase.

B) Enzyme activity would steadily decrease.

C) Enzyme activity would increase and then decrease.

D) Enzyme activity would remain constant

Explanation

This question is asking about a perennial MCAT favorite – enzymes. The test will expect you to know many of the common enzymes found around the body. You’ll also be expected to know the basics of how enzymes function, and the effects of inhibitors (both competitive and non-competitive!), pH, and temperature on enzyme activity. This question is a typical example of how the MCAT will ask about temperature.

We’re told the enzyme is normally found at body temperature. Thus it’s safe to conclude that the optimal temperature for lipase is around 37ºC. Then question then says the beaker starts at room temperature. On the MCAT, that means 25ºC.

Since the beaker is initially colder than the enzyme’s ideal temperature, its activity is going to be lower than normal. As the temperature is increased towards 37ºC, enzyme activity will increase. However, once the beaker gets hotter than that, the enzyme will start to denature and its activity will drop off quickly. Thus, the correct answer is (C).

If you couldn’t recall information about enzyme activity in particular, you should definitely guess. Remember, don’t leave any questions blank on the MCAT! Here, the smart move for guessing would be to eliminate answer choice (D) and then guess among the remaining choices. Chemical reactions are greatly affected by temperature and reactions that use enzymes are no different. If you remembered that basic chemistry fact, you can narrow things down a bit, make a smart guess, and move on.